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tonight, on a special "20/20" -- caught. breaking news, the most wanted man in america. suspect number two, now found. the incredible drama of the last few hours. dozens of shots, cornered in a boat by the police and taken alive. >> suspect is in custody. nobody has come into the perimeter. >> who is the 19-year-old honor student, the popular high school wrestler, who brought a major american city to a standstill? friends in shock. >> it never seemed like there were any warning signs. >> what changed after 12 years in this country, to turn the brothers into killers? contradictions between their uncle. >> being losers.

not being able to settle themselves. >> their aunt. >> the picture was staged. >> and our exclusive phone conversations with their defiant father in russia. how two unanimous men in caps gradually became known as killers with names, history and grudges, while dozens of their victims still fight for their lives. reporting live from boston, elizabeth vargas. >> good evening. what an evening it has been here in boston tonight. we heard president obama speak a short time ago about the capture of the second boston marathon bomber, allegedly. calling the suspects, quote, small, stunted individuals. but now a mood of celebration has broken out on the streets of boston. we have had people who have been locked inside their homes all day long, 1 million of them who are out on the streets right now, many of them cheering, waving flags a mood of

celebration that almost rivals the red sox winning. the news has been changing almost minute by minute. but right now, this is what we know. the marathon bombing suspect, dzhokhar tsarnaev, is now in custody. found hiding in a boat. he is conscious, in serious but stable condition. at a nearby hospital. get the very latest, go to all of our abc news team, but start with linsey davis who was in the neighborhood where the arrest went down. heard all the gunshots breaking out. now has been listening to all the celebrations. good evening, lynn lindsy. >> good evening, elizabeth. many of those crowds just now starting to disperse. we're talking about a group of people who has been waiting for a reason to cheer since monday. tonight they got it. they started applauding as the police started filing down the street shortly after hearing the

gunshots. they started yelling, go get them. they started cheering. then on the way out, they were saying, you got 'em. we got 'em. the cheers erupted as the ambulance went by. people believing inside the ambulance was the man known as suspect number two. and at that point, people started yelling, boston pride, boston strong, bpd for boston police department. usa, usa. they were singing "sweet carolina," the star-spangled banner and the police responding in kind. high-fiving those stand big. they were giving them fist pumps and thumbs up. people joyous and relieved, elizabeth. >> joyous and relieved after a very long week. thank you, linsey. i want to read a tweet from the boston police department tonight. it reads, captured in all caps. the hunt is over. the search is done. the terror is over and justice

has won. suspect in custody. and for more on how all that went down tonight, we'll go to abc's brian ross who has been following this story all week. the manhunt and finally last night the gunfire and today the brian, how did thi man who was hidingr a boat in somebody's backyard? elizabeth. as you say, it began with a gunfight and he fled on foot last night. this morning, officials put a lockdown on nol wa, lockdownropa.ol wa, no one was allowed out o this man. at 6:30 they called offthe search and conceded, he got away. we couldn't find him. then, just 25 minutes later, a resident in this area, now relieved from being locked in, went outside to walk the dog and noticed in his prized boat in there was blood on it. he climbed up to take a look, opened the tarp and inside was a man all blood

he ran away. called the police. they responquic and inside was suspect number two. they used robots to rip the tarp off the top of the boat and shock grenades to disorient him. there was a brief exchange of gunfire. and then, the fbi s.w.a.t. teams moved in and took him into custody alive. and he's on his way to a hospital now, in serious but stable condition, elizabeth. >> and was he armed, brian, when they took him in? >> reporter: he did have a weapon. there was an exchange of fire. but he had no explosives. just final weapon. used up all his explosivior to that time. >> all right. an example of how fast-moving. thank you, brian, all this was happening. 25 minutes between the time the police lifted the all-clear to let people out of their homes for the first time all day long. and then later on, just 25 suspect in somebody's b all this is amazing, considing the veryat tm dzhokhar owed two days after the bombing. it was, quote, i'm a stress-free kind of guy.

well, that certainly didn't end up being the case. tonight, after a manhunt that was the most massive since 9/11, one that was well underway by the time most of the people were waking up this morning. >> this is actually gunfire exchange between -- >> who knew the week would end almost as deadly as it began? boston awoke to the news of more chaos and more carnage. in the wake of a predawn high-speed chase, one officer killed. another wounded. suspect one is dead. suspect two at that point on the run. >> police and federal authorities are in an active search in watertown for an armed and dangerous suspect. >> police are on high alert. boston residents are paralyzed. they discover they will not be leaving home this day. they are living under lockdown. >> you have to stay in your homes. stay in place. there's a major crime scene down there. it will take some time. >> law enforcement hone in on two towns -- 7:20 a.m. in cambridge, police search a home

where they believe the two brothers lived. >> and in watertown, the last place where the last suspect was seen, police recovered 200 spent rounds. evidence that homemade bombs and a pressure cooker. but no evidence of the suspect. the typically tranquil boston suburb is swarming with s.w.a.t. teams. military units searching house to house. while residents look out their windows at the surreal sight. >> yeah. he is in our garage right now. >> we've had s.w.a.t. teams police patrolling the neighborhood in our backyards, doing house sweeps. feel like i'm in middle of a movie set. >> residents are trapped. many are terrified. >> my feeling is until this guy is found, i'm just not feeling okay. >> at what would be rush hour, massachusetts governor deval patrick tells boston residents to shelter in place. >> in other words, stay in doors, with their doors locked and not to open the door -- >> it is an unprecedented halt

to a city of more than 600,000 people, hundreds of thousands more in the neighboring towns. schools, universities, the subway, all businesses, closed. a city at a standstill. >> somebody described it as a blizzard without the snow. >> you know what, i think the word surreal is overused, but it fits today. >> homeward bound bostonians are glued to the television for any news. sharing information by text, telephone an internet. >> keeping the doors locked and your kids to overreacting to what's a scary situation. >> 9:45 a.m., president obama meets with his national security team. the fbi releases a wanted poster for suspect number two, know known as dzhokhar tsarnaev. digital billboards quickly posted. the uncle of the suspect holds an emotional press conference. >> i never would imagine children of my brother would be associated with that. >> the search widens to new jersey.

the fbi removes evidence from the home of the suspect's sister. the 6:00:p.m. the stay at home order is lifted. there is no all-clear. >> my message to the suspect is give himself up. >> approximately 7:00 p.m. gunshots in watertown, reports of a suspect found in a boat. when we come back, who are these two brothers, suspects number one and two? and what turned seemingly normal americans into alleged terrorists. stay with us. and now, in the rest of my home. ziploc helped me turn this closet... into this closet. i tripled my storage space. with ziploc space bag just pack your items... seal the ziploc space bag double zipper... and vacuum out the air through the valve.

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"20/20" continues from boston. here, again, elizabeth vargas. >> so, who are these two brothers? and what changed them from regular bostonian boys into alleged bombers?

dan harris has been working with his sources all day to find out. >> i never, ever would imagine that somehow, the children of my brother would be associated with that atrocity. we're devastated. we're shocked. >> reporter: even their own family members are asking the question nobody else seems to be able to answer tonight. why? >> what do you think provoked this? >> being losers, hatred to those who were able to settle themselves. these are the only reasons i can imagine. >> reporter: so, why did 26-year-old tamerlan tsarnaev and his 19-year-old brother dzhokhar allegedly commit one of the most heinous acts of terrorism in america since 9/11? >> absolutely shocking. the high school student that i knew and the high school student that all my classmates knew is the exact opposite of the person that's been committing these

crimes and doing these horrible things. >> didn't really seem like the type to be, like, that would harm a fly. >> reporter: the brothers are originally from a war-torn part of russia. the family fled that region in 2002. >> chechens were persecuted. there was a manhunt for us at one point. they were about to annihilate us. >> reporter: their american experience began as a classic tale of immigrant assimilation. their father found work in an auto body shop. their mother became a cosmetologist. and the boys flourished in boston's academic environment. dzhokhar in particular excelling at the cambridge rindge and latin school. >> he took a lot of honors classes. he was not someone that didn't try hard. he did try hard. >> reporter: he made friends, took drama classes and impressed people as gentle and subdued. >> hard to believe that someone that was so friendly and funny just a couple of years ago could

have done this. >> reporter: he was some what of a jock. he became the all-star captain of the wrestling team. >> he was completely americanized. and really a sweetheart of a kid. >> reporter: his older brother, tamerlan, a bit rougher around the edges, however. after high school, tamerlan attended bunker hill community college for three semesters. but his real passion was boxing. he fought his way into the new england heavyweight golden gloves championship and had dreams of representing america in the olympics. but in 2009, tamerlan was reportedly arrested for assault and battery against his girlfriend. the charge was later dismissed. the caption to these boxing photos, found on the internet, may also shed some light on tamerlan's mindset. this one reads, "i don't have a single american friend, i don't understand them." and this, "there are no values anymore. people can't control themselves." meanwhile, by 2011, dzhokhar seemed to be on top of the world.

he graduated high school. and the city of cambridge honored him with a $2,500 merit award. he enrolled in the university of massachusetts at dartmouth. lived in a co-ed dorm and played weekly soccer matches with his friends. >> we played soccer every week. mondays. not this monday, the monday before, the last time i played soccer with him. he actually gave me a ride to the place. >> i mean, you could tell he was a little bit of a pothead. but i mean, besides that, he was just a quiet guy. there wasn't much to him. >> reporter: while there were no signs of trouble, but there was something darker going on with dzhokhar's online alter ego. look at the alleged tweets. in which he says -- september 10th, you have to be here tomorrow is, party at my house. and, never underestimate the rebel with a cause. death is the destroyer of all pleasures. two years ago, the fbi interviewed tamerlan on behalf of a suspicious foreign government, though they found nothing derogatory. by the beginning of this year, the family seemed to be fracturing.

the father returned to russia for health reasons. tamerlan spent the first half of 2012 back in russia himself. what he was doing there remains unclear. >> give me evidence. all you showed me, man's face in a hat standing like this. what else? >> ah, my two sons are really innocent. i'm like 100% sure that this is a setup. >> reporter: the boys' mother and their aunt defended them today. and this woman, allegedly a sister living in new jersey, fended off the media. >> i'm very, very upset right now because i lost -- listen, i'm so sorry. >> they're related. they're brothers, right? >> no, they're not. >> reporter: and while so many questions remain about what finally turned these brothers into alleged terrorists, their family is now left with the difficult task of clearing their name. >> my family, my family associated. we're not requiring forgiveness in this family.

people are ashamed. he put shame on our tsarnaev's family. he put a shame on our family, the tsarnaev family. he put a shame on the entire chechen ethnicity. because everyone now names the play with the word chechen. so, they put that shame on the entire ethnicity. >> clearly, family members of these two suspected bombers torn apart with differences on whether they are guilty or innocent. i'm now joined in new york with bianna golodryga who is fluid with russia. you spoke to the american tv reporter to speak to the father. the only american tv reporter to do so. you broke the news to him that his younger son was taken alive. >> that's right, elizabeth. i spoke with anzor five times today. and let me summarize our lengthy conversations because his initial demeanor was completely different from how our last conversation ended. initially he was confused by the news. he had told me that he spoke within his sons after the monday

bombings. said they were calm and hadn't been there is what they told him. his sons could never perpetrate such a crime. they were calm men, peaceful men, didn't have any military training. then, when i later spoke with him, he started bringing up framed. framed was a term he kept using. he didn't believe that this was happening. he wanted proof, pictures of what his sons were being accused of doing. he had lived in the u.s. for ten years. dzhokar had moved here when he was 7 years old and was raised -- basically raised here in this country. the fourth conversation we had -- the third mind you, he actually called me. we were live on set, breaking news, he called me, texted me, asking me for updates as to what was happening. he didn't have all of this information in russia. so, i gave him the latest of what we knew what was happening with his son. again he was still confused and shocked and disbelief. our fourth conversation turned to anger. actually we recorded this conversation, the fourth one we

had when i asked him point-blank what he had to say to his son at that moment. >> translator: if he is watching, i want to see him alive and i want to know the truth, what, when, why, where. this is a setup. i don't believe it. they're being framed. i don't believe this. it is not possible. not possible. >> not possible. you can hear the anger in his voice. then, elizabeth, of course our last conversation was just a couple hours ago when we got word that his son had been captured. he was alive. i called him. a different state of mind. he was emotional. he started to cry. he said, thank god, thank god. he said he is on his way to the u.s. he said unfortunately i lost one son. i'm happy to hear i still have another one alive, elizabeth. >> wow. and bianna, also he said -- to his son who is still alive, cooperate fully. tell police everything. >> right. everything.

>> all right. bianna golodryga in new york. thank you so much. we'll be right back on this special edition of "20/20," live from boston. ♪

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we are live back here in boston. just moments ago, we got a dramatic image the first image of the bombing suspect, number 2, dzhokhar tsarnaev being arrested tonight. you see him there, this photo of him has been verified by the alcohol tobacco and firearms department. this is him, he is being on the ground being tended to by a medic. he was seriously hurt is in surgery already at a hospital. here you see the very first photo being arrested in a dramatic confrontation just 25 minutes after the lockdown on 1 million people was lifted here in the boston area. to get a complete picture of how this young man and his brother became coming into focus for the fbi, we need to go back to the

very beginning of this story. monday morning. 23,000 runners were shaking out their legs and waiting for the starter pistol to go off here in boston. the finish line just behind me here. hours later, 3 people dead, 170 injured. and four days later we would all know the name tsarnaev. we look at the week when a marathon turned into mayhem. >> reporter: roughly six hours before these terrifying blasts on monday -- all eyes were focused here. hopkinton, massachusetts -- the starting line of the legendary boston marathon -- a 26.2 mile course that winds its way through leafy suburbs before reaching downtown's copley square. sun, light cloud cover, 50 degrees -- perfect day for a marathon.

shortly after 9:00 a.m. -- just over 23,000 runners begin their journey. at 11:58 a.m., the winners cross the finish line. >> 2013 boston marathon champion. >> reporter: over the next few hours, thousands more, exhausted and triumphant, do the same. 2:37 p.m., security cameras capture these images of two men snaking their way through the thick crowd gathered along boylston street, one in a black hat, tamerlan tsarnaev. the other in white, his younger brother, dzhokhar. 2:50 p.m. -- dual explosions 550 feet apart. the first here, the second here. >> something just blew up. run. >> reporter: in an instant, chaos and carnage. spectators and runners in both locations knocked to the ground. >> instantly it was the

brightest light and loudest ting in your ear. >> everybody started running. panicking -- >> it was very loud the ground shook and you could just feel it going down through you. >> reporter: as the smoke clears, cameras from all angles capture what looks like a war zone. sidewalks painted in blood, victims paralyzed, in shock and confusion. >> i saw quite a few casualties coming back. one guy with his legs gone at the knees. ankles and feet missing, shrapnel wounds on the side of the head. >> reporter: what did the smoke cloud and the kind of injuries you heard about in the beginning tell you about what had happened? >> when we saw the film and saw that it was white cloud, that meant it wasn't a heavy-duty explosive. that meant it was a smaller, more improvised, more amateur device. >> reporter: just after the blast, david green takes this photo that would later prove critically. >> i immediately, i don't know why, but i pulled out the phone of my packet and snapped a quick picture. >> reporter: as many flee, there

are others who run toward the epicenters. police, marathon volunteers in and good samaritans, like michael chaise, seen carrying a little girl named jane richard. >> it was pretty intense. i didn't think twice. i was just looking to help people. >> reporter: so was cowboy hat-wearing, carlos arredondo, captured wheeling badly wounded 27-year-old jeffrey bauman, now an iconic image of this tragedy. >> my first instinct was the run across and start helping people. >> reporter: law enforcement filled the now-evacuated area and secure a vast and intricate crime scene. the injured are rushed to area hospitals where doctors like george velmahos spring into action. >> we had to do four amputations. quite frankly, they were -- they were almost completely amputated by the bomb blast. >> reporter: at 4:12 p.m., reports of another blast, near jfk library in dorchester. later revealed to be an electrical fire. then it spreads. cities in the northeast catch the same case of the jitters.

new york city and the capital go on high alert. 6:10 p.m., with pennsylvania avenue closed to pedestrians, president obama offers condolences to victims in boston. >> we'll find out who did this. we'll find out why they did this. any responsible individuals, any responsible groups will feel the full weight of justice. >> reporter: tuesday begins with more heartache. 176 confirmed injured and the death toll now at 3. including 8-year-old martin richard. turns out, he's the older brother of jane, seen carried from the scene by michael chase. 9:30 a.m., deval patrick and fbi officials appeal to the public for any videos they have of the marathon. no detail is consider to do small. >> we will go to ends of the earth to identify the subject or subjects who are responsible for

this despicable crime. >> reporter: 11:30 a.m., president obama speaks to the country again. this time using the word everyone is waiting to hear. >> the fbi is investigating it as an act of terrorism. >> reporter: meantime, dzhokhar tsarnaev in a state of agitation, goes to his auto shop to pick up a white mercedes. >> before he was very polite, in a million years that you could, you know, notice that the kid was evil person. >> reporter: photos now appear online of what's believed to be components of the bombs. a mangled pressure cooker and a tattered black backpack. there are also photos of a circuit board and batteries, quickly linked to a distributor of a popular children's remote control car. 2:00 p.m., krystle campbell becomes the second victim identified. >> we are heartbroken at the

death of our daughter krystle campbell. it still doesn't make any sense. >> reporter: as families of the victims grieve, dzhokhar tsarnaev later tweets, nowadays everybody wanna talk like they got something to say but nothing comes out when they move their lips, just a bunch of gibberish. wednesday, 9:30 a.m., as dzhokhar attends class, word spreads that authorities are closing in on a suspect. >> this is a fast-breaking investigation with a major breakthrough already. >> reporter: the internet is on fire with speculation. websites, like 4chan are dissecting photos of the scene, raising suspicions about faces in the crowd. all, including this young man, turn out to be not involved. >> if you look at it, it wasn't me. >> reporter: 1:30 p.m. -- >> wolf, we have information an arrest has been made.

>> reporter: cnn erroneously reports the arrest has been made and will be announced shortly by the fbi. but that press conference never happens because a bomb threat empties the courthouse. the final victim is identified as lu lingzi. wednesday ends with yet another tweet from dzhokar tsarnaev saying i'm a stress-free kind of guy. thursday morning, with the bomber still on the loose, the president and first lady arrive in boston for an interfaith service in honor of the victims. >> your country is with you. we will all be with you as you learn to stand and walk and, yes, run again. of that, i have no doubt you will run again. you will run again. >> reporter: with no news from the feds, frustrations are growing. but later that day, the break everyone had been waiting for. stay with us. when we come back, a

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thursday afternoon, 5:20 p.m., amid a flurry of rumors and growing impatience, the fbi finally shows its hand. >> today, we are enlisting the public's help to identify the two suspects.

>> reporter: those now-famous images. they are identified as suspect 1 and suspect 2. they appear to be associated. >> reporter: for the first time, the world sees the faces of evil. the hope is the public will help the fbi flush them out. >> somebody out there knows these individuals as friends, neighbors, co-workers or family members of the suspects. >> we have never seen anything quite like this before where they are actually asking people not to just to look out for somebody but to turn in their cameras. >> reporter: minutes later, the fbi website crashes from so many clicks. tips make their way in fast and furious. among them, david green says he has a picture that may help. the fbi releases that shot -- a clearer image of suspect 2. turns out many people not only recognized dzhokhar tsarnaev but quite a few were his classmates. but they hadn't called authorities because they couldn't believe the guy they

knew could have been a bomber. >> he was a very nice kid. i got along with him very well. >> i can't say this enough, he's just not the guy. he's not the kind of guy to do that. >> didn't expect anything like this from him. >> reporter: as the night grows late, and bostonians go to bed, there is still no word if any actionable leads have come in. later that night, the silence is broken. shots are fired and 26-year-old m.i.t. police officer sean collier is found fatally wounded. >> an m.i.t. police officer was shot and killed in the line of duty tonight. >> reporter: suddenly the campus is swarming with police and news crews. could this be connected to the bombings? >> reporter: moments later, not far away, a man driving a black mercedes suv says he's attacked at gunpoint by two men. he later tells police the men revealed themselves as the bombers and dropped him unharmed at a gas station. police are in pursuit of the mercedes in a high-speed chase through residential neighborhoods. >> there were probably about

half a dozen police cars that immediately got up and took off in the other direction. it was incredibly fluid situation. >> reporter: the gunmen, tossing grenades from the stolen car are headed west. they end up about five miles away in the small community of watertown. a wild gunfight erupts. >> i counted about 40 to 45 police officers coming down in their cars. so, i got out on the balcony to see what i could see, at which point i heard a very, very loud explosion, a boom. i didn't see it. but as i looked up in the sky i could see it lit up the entire sky around watertown. >> reporter: in the melee, a transit cop is seriously injured. and suspect number one, tamerlan tsarnaev, runs toward the police. minutes later, while escaping police in the stolen vehicle, dzhokhar runs over his own brother, who later dies. dzhokhar eventually flees on

foot. >> police and several authorities are in an active search in watertown for an arm and dangerous suspect. >> reporter: around 2:00 a.m., police begin a robocall to every person in town with a warning -- stay inside. don't open your doors. >> remain indoors until further notice. >> i got a robocall from the police. and i'm like, oh, my god. this is watertown. that's not supposed to happen here. >> reporter: for an entire day, close a million people are ordered not to leave their homes. by evening, the lockdown is finally lifted. 9:00 p.m. news that the suspect is in custody. yet the investigation is far from over. >> well, the fbi has an enormous task ahead of them. even once they catch this guy, because they have to find all of his known friends, all of his known associates, the same with his brother. this case will be an open case for weeks, if not months in the future. next, the other two people

everyone is talking about tonight. complete strangers, runners, one who completed the race once the bomb stopped. >> and i just took off my medal and looked at her and said, you know, you're a finisher. and i just put it around her neck. >> now reuniting for the very first time to show how evil didn't win. >> thank you so much. er er neck. er neck. ok! now reuniting for the very first now reuniting for the very first time to show how evil didn't win. time to show how evil didn't >> thank you so much. that didn't take very long did it! this spring, dig in and save. that's nice, post it. already did. more saving. more doing. that's the power of the home depot. dig in and save with earthgro mulch, a special buy at 3 bags for just 10 bucks.

if you've been watching our on going coverage on abc news all day today, you've met one of your newest colleagues, byron pitts. we're happy to welcome you to the "20/20" family. even under these incredible circumstances. you have an amazing story of a very moving reunion. >> it's hard to put into perspective, how sit possible that two young men could allegedly do so much harm, killing innocent people and changing thousands of lives, all of it, in an instant.

the longest week in the wounded city of boston, attacked monday. >> my god. >> locked down friday. we're getting answers tonight, but certain questions will always linger. one of the hardest, one that echos after every calamity, what if? what if krystle campbell had not taken off this particular day from the restaurant where she worked so hard just to cheer and celebrate the spring sunshine? >> this doesn't make any sense. >> reporter: what if a mother and father in china had not scrimped and saved and bet on their bright daughter, lingzi lu, their only child, sending her off to study at a university in a place on the other side of the world. what if a little boy with an adorable smile, martin richard, and his little sister had not gone for ice cream?

in dorchester, as a tribute to martin, they stopped the clock. but no one can turn back time. you ask the question, 23,000 times, once for every runner, what if? so, you come to boston to see your son run in the boston marathon. >> yeah. absolutely. i wouldn't have missed it. >> what if linda witt had not flown all the way from wisconsin to see her son, bill, running in his first boston marathon? she snapped these pictures as bill turned down the home stretch. then decided at that moment to bolt for the finish line. my son. at the finish line. i wanted to hold him and -- i wanted to be there for him. >> reporter: that was the moment for you. >> that was the moment. it was just like that. i got to see him, you guys. i'm going to go. >> the first blast struck linda. >> then there was another blast. saw the smoke. >> reporter: hard for your still?

>> you really don't know what to do. and then -- right in front of me there was this poor gal and she just kind of looked like a broken doll. >> reporter: ironically linda's son, not a scratch. she is the one who got hurt. >> at this point, we saw her pants all ripped up. she said she couldn't hear us. >> reporter: she lost 50% of her hearing in the blast. doctors say it's temporary. but the memories, the faces they will linger a lifetime. and you saw what? >> fear. fear. >> reporter: before the fear, for laura, all those miles on monday with the last leg of a long journey. >> a couple years ago if you had said, you're going to run a marathon in a couple years i would have laughed and said you're crazy. i couldn't run a mile. >> reporter: hobbled by a bad knee she considered quitting.

>> they were medical tents along the way that i looked at, brains are telling me to stop. my heart was telling me to keep going. >> reporter: she wonders what if she had not been slowed by the very good fortune of a bad knee. if your leg had been okay, when would you have got on the the finish line? >> if my knee was okay, i was on pace to run a 4:15 marathon, which would have put me at the finish line at 2:55. yeah. it's crazy. my family would have been at the finish line fating for me. >> reporter: your parents? your siblings? your boyfriend? your friends? >> everyone. i don't know exactly where my family is. but i know they're in somewhere in that four or five-block span on boylston street at the finish line waiting for me. >> reporter: brent finished the boston marathon, 40 minutes before the blast. blocks away, he was in the satisfaction of finishing the 26-mile course for the first

time. >> it's a runner's dream to run boston. >> reporter: you got to live that dream. >> yeah, i did. >> reporter: he received a medal to prove it. how important is that medal to you? >> when you lean down and a volunteer puts it around your neck, it's your little chance to feel like -- just the sense of accomplishment. >> reporter: it is a moment laura wellington will never know. stopped a heart breaking half mile short of the finish, she misses out a treasured medal. word finally reaches her, her family has been spared. >> i just kind of walked over here and just sat down and just lost it. i just was so emotional. >> in that instant, brent and his wife pass by. >> the next thing she knows she takes me blanket. >> he took the medal off the neck. and he asks me, did you finish? i said no. >> i looked at her and i said,

you're a finisher. and i just put it on her neck. and we walked away. >> i was sobbing. like, i just couldn't get out anything. i couldn't say thank you. i couldn't tell him what i -- like how much it meant to me. >> really it was just an opportunity to express to her in her moment of loneliness that you're not alone. >> reporter: before laura could say thanks or even get his name, brent was gone. so, she thanked her mysterious benefactor on facebook. >> i put the thing on facebook yesterday just thinking a couple of my friends would circulate it. a couple thousand people shared it. tens of thousands and then this morning i woke up and it was over 100,000 people had shared it on facebook. it was unbelievable. >> reporter: word of the post reaches brent cunningham, by then all the way back home in alaska. but for something like this, an online thank you note falls little short.

so, we bought brent a ticket and he agreed to turn around and take another marathon flight back to boston. we have someone who wants to say hello to you. >> oh, god. >> i love you. >> thank you so much. >> you're welcome. >> thank you. >> reporter: which brings us back to, what if? of course, there is no answer. but there is hope. some would say on monday, evil won. >> at times you might feel they might have won the battle. but they're not going to win the war. love wins. game over. >> reporter: this has been a week of powerful emotions in boston. shock, anger, fear. tonight, some measure of relief. elizabeth, the headline in "the boston globe" tomorrow morning may say it best, nightmares end. >> sure does. byron, what a fantastic report.

thank you so much. and we'll be right back. ♪ ♪ ♪ ♪ ♪ the new blackberry z10. with time shift and blackberry balance. built to keep you moving. see it in action at blackberry.com/z10

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♪ a city celebrates the end of a nightmare. new details on the capture of the suspect.

>> and the new level of security at at&t park. how the bombing in boston has changed the way we will see a